Spark plug ports???
 

Hi all,

I've decided to try my hand at rebuilding the motor I pulled out of my 81', during the tear down I noticed the size of the spark plug ports into the houseing! Is there a particular reason the trailing port is so much smaller than the leading? would having slightly larger ports not help? How about having a small tapper to the wholes?
Keep in mind I'm new to the internal workings of a rotary and would like to expand my knowledge, so any info on this matter would be helpful!!


Thanx

Matt

trailing is mostly for smog reasons and is there to burn any left fuel.

late rotarys used only one spark plug per housing.

Don't mess with what works. As mentioned, the trailing is mostly for smog, disabling it reduces performance only a few percent.

The trailing ignition hole is smaller than leading so the heat from the trailing spark plug won't transmit to the combustion chamber and pre-ignite the fuel mixture. Since the rotor passes the trailing plug first. This is also why Mazda started running colder plugs on the Trailing.


I've never head of enlarging this hole.

Actually the real reason it is smaller has nothing to do with heat. If that were true all piston engines would be screwed. Remember that there is pressure on each face of the rotor. When the apex seal is crossing the leading spark plug hole, the pressure on each side of the rotor is fairly equal which means there isn't much in the way of leakage through the spark plug hole around the apex seal. The trailing location however is different. The pressure on the chamber in front of the apex seal is much higher than it is in the chamber behind it. If the trailing spark plug hole was larger, pressure from the front chamber would bleed off into the following chamber at this point. They need to keep the hole as small as possible to prevent this from happening. There is a Mazda graph showing this floating around somewhere.

The reason why the trailing plugs are colder is for an entirely different reason than spontaneously combusting the incoming charge. Again, that isn't an issue or else piston engines would all be screwed.